Network operators are replacing conventional time-division multiplexed (TDM) based transport networks with Ethernet based transport networks, which can allow transport of a wide range of traffic types. Ethernet-based networks comprise a network of Ethernet switches.
Technologies which allow the use of Ethernet switches in carrier networks are Provider Bridge Networks, standardised by the Institute of Electrical and Electronics Engineers as IEEE 802.1ad, and Provider Backbone Bridges (PBB), standardised as IEEE 802.1ah. Both of these technologies use Virtual Local Area Network (VLAN) tags to identify traffic belonging to particular customers. PBB is a technology which allows for layering of the Ethernet network into customer and provider domains with complete isolation among their MAC addresses. In this way, a customer's traffic can be carried transparently across a carrier's Ethernet network.
Ethernet networks can be used in a connection-oriented manner using techniques such as Multi-Protocol Label Switching Transport Profile (MPLS-TP) or Provider Backbone Bridge Traffic Engineering (PBB-TE), or in a more conventional connectionless manner. When used in a connectionless manner, the nodes of the Ethernet network use techniques such as flooding and learning to establish a loop-free path between the source and the destination for the configured service. A distributed protocol such as the Spanning Tree Protocol (STP) can be used. In the event of a network disturbance, such as a fault or failure of a link or node, STP will recalculate a loop-free topology. In this specification, the term Ethernet Virtual Connection (EVC) is used to describe a traffic flow across a Carrier Ethernet network between two User Network Interfaces (UNI).
From a fulfillment perspective, traffic tagged with the relevant Virtual Local Area Network (VLAN) tags is configured on all of the ports of switches that can be involved in any of the possible packet routes that the spanning tree protocol can calculate. This gives provider bridge networks a high level of unpredictability in determining where the packets are really flowing in the network for a given Ethernet service at a given time. This is a problem from a service problem detection perspective as, at the time a fault on the data plane is detected by the NMS/OSS system, the traffic could already have been reverted on another route by the spanning tree protocol. Considering also that Ethernet networks are based on statistical multiplexing, it means that it is problematic to identify if a given Ethernet service is affected by traffic degradation or traffic disruption.
One of the factors to help deliver carrier-grade performance in an Ethernet network is to provide OAM (Operation Administration and Maintenance) capabilities that allow the service provider to detect, isolate and eliminate faults in the network to prevent service traffic degradation and, in the worst case, service traffic disruption that highly impact the committed SLA (Service Level Agreement). The IEEE has standardised protocols and practices for Operations, Administration, and Maintenance (OAM) for paths through 802.1 bridges and local area networks (LANs) in IEEE 802.1ag, “IEEE Standard for Local and Metropolitan Area Networks Virtual Bridged Local Area Networks Amendment 5: Connectivity Fault Management”. IEEE 802.1ag defines the concept of service OAM, which allows the configuration of Maintenance Entities associated to the Ethernet Service in order to detect if something goes wrong on the Ethernet Service end to end through some connectivity verification procedures. However, service OAM has some limitations. There are limits on the number of Maintenance Entities that are configurable in a network element, and therefore this approach may not be scalable to give a protection for all the configured Ethernet services.
The present invention seeks to provide an alternative way of monitoring a Carrier Ethernet network.